On Wed, 2011-09-07 at 16:30 -0400, Steve Grubb wrote: > On Wednesday, September 07, 2011 04:23:13 PM Sasha Levin wrote: > > On Wed, 2011-09-07 at 16:02 -0400, Steve Grubb wrote: > > > On Wednesday, September 07, 2011 03:27:37 PM Ted Ts'o wrote: > > > > On Wed, Sep 07, 2011 at 02:26:35PM -0400, Jarod Wilson wrote: > > > > > We're looking for a generic solution here that doesn't require > > > > > re-educating every single piece of userspace. And anything done in > > > > > userspace is going to be full of possible holes -- there needs to be > > > > > something in place that actually *enforces* the policy, and > > > > > centralized accounting/tracking, lest you wind up with multiple > > > > > processes racing to grab the entropy. > > > > > > > > Yeah, but there are userspace programs that depend on urandom not > > > > blocking... so your proposed change would break them. > > > > > > The only time this kicks in is when a system is under attack. If you have > > > set this and the system is running as normal, you will never notice it > > > even there. Almost all uses of urandom grab 4 bytes and seed openssl or > > > libgcrypt or nss. It then uses those libraries. There are the odd cases > > > where something uses urandom to generate a key or otherwise grab a chunk > > > of bytes, but these are still small reads in the scheme of things. Can > > > you think of any legitimate use of urandom that grabs 100K or 1M from > > > urandom? Even those numbers still won't hit the sysctl on a normally > > > function system. > > > > As far as I remember, several wipe utilities are using /dev/urandom to > > overwrite disks (possibly several times). > > Which should generate disk activity and feed entropy to urandom. I thought you need to feed random, not urandom. Anyway, it won't happen fast enough to actually not block. Writing 1TB of urandom into a disk won't generate 1TB (or anything close to that) of randomness to cover for itself. > > Something similar probably happens for getting junk on disks before > > creating an encrypted filesystem on top of them. > > During system install, this sysctl is not likely to be applied. It may happen at any time you need to create a new filesystem, which won't necessarily happen during system install. See for example the instructions on how to set up a LUKS filesystem: https://wiki.archlinux.org/index.php/System_Encryption_with_LUKS#Preparation_and_mapping -- Sasha. -- To unsubscribe from this list: send the line "unsubscribe linux-crypto" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
